Sex-related risk for group A streptococcal bloodstream infection in Queensland, Australia, 2000–2023

BACKGROUND: Although several studies have found males to be at increased risk for development of invasive group A streptococcal (GAS) infections, the determinants of this excess risk are not well-defined. The objective of this study was to examine sex as a risk factor for GAS bloodstream infection (BSI) in a large Australian population. METHODS: All residents of Queensland, Australia with GAS BSI identified within the publicly funded healthcare system between 1 January 2000 and 31 December 2023 were included. RESULTS: 4,043 incident GAS BSI infections occurred for an incidence of 3.8 per 100,000 population. Males were at significantly increased (relative risk; RR, 1.22; 95% confidence interval; CI, 1.15-1.30) but this was dependent on age and pregnancy status. Among those aged < 15 and >35 years, males were at higher risk, whereas females were at higher risk between ages 15-35 years. Among the age cohort of females aged 15-49 years, pregnancy was associated with a 9.0-fold (95% CI, 7.5-10.7) higher risk for GAS BSI as compared to non-pregnant females, with the latter group at similar risk (RR 0.9; 95% CI, 0.8-1.0) as compared to males of this age group. Although clinical determinants varied significantly across age groups, sex-related differences within age strata were limited, except among pregnant women. The all-cause 30-day case-fatality rate was 9.5% and was not significantly different between males and non-pregnant females. No deaths were pregnancy-associated. CONCLUSIONS: Although the overall incidence of GAS BSI is higher in males, females aged 15-49 are at marked excess risk that is pregnancy-associated.